1. Technical Field
The present invention relates to a recording apparatus.
2. Related Art
A recording apparatus (so-called ink jet printer) which performs printing by ejecting an ink (droplet) onto a recording medium so as to form dots is known. Such a recording apparatus includes a recording unit and a recording head. The recording unit can relatively move a print medium in a main scanning direction and a sub-scanning direction. The recording head is attached to the recording unit. The recording head includes a plurality of nozzles. In the recording apparatus, an ink is ejected from each of the nozzles. JP-A-2012-152957 discloses a configuration in which a plurality of recording heads is disposed in zigzag in a recording unit in such a recording apparatus.
As a forming method of dots in the above-described recording apparatus, “a full-overlap method” in which, regarding all raster lines, dots on the same raster line are formed by multiple times of main scanning is known.
FIG. 1 illustrates an example of a recording unit U in which a plurality of recording heads Hd is disposed in zigzag. In FIG. 1, a main scanning direction of the recording unit is indicated by an arrow which is denoted by X, and a sub-scanning direction of the recording unit is indicated by an arrow which is denoted by Y. A direction perpendicular to both of the main scanning direction X and the sub-scanning direction Y is referred to as a depth direction Z. Among the plurality of recording heads Hd which are disposed in zigzag in the recording unit U, a set of recording heads Hd disposed on the right side (dot-hatching in FIG. 1) is referred to as a “right-side head”, and a set of recording heads Hd disposed on the left side (slash-hatching in FIG. 1) is referred to as a “left-side head”. In FIG. 1, the right-side head is indicated with being surrounded by a one-dot chain line, and the left-side head is indicated with being surrounded by a broken line.
FIG. 2 is a diagram illustrating a problem in the related art. In FIG. 2, each of dots formed on a recording medium by nozzles of the right-side head is presented by a thick-bordered circle, and each of dots formed on the recording medium by nozzles of the left-side head is presented by a thin-bordered circle. Each pixel which is formed on the recording medium by a dot when the recording unit U is moved forth in the main scanning direction X is presented by a hatched quadrangle. Each pixel which is formed on the recording medium by a dot when the recording unit U is moved back in the main scanning direction X is presented by a blank quadrangle.
As illustrated in FIG. 1, in a case where printing is performed with the recording unit U in which a plurality of recording heads Hd is disposed in zigzag, by using the above-described full-overlap method, the followings may be mixed on the recording medium.
First type of raster line (L1, L2, L3, L4, L5, and L7 in FIG. 2) in which both of dots formed by the nozzles of the right-side head and dots formed by the nozzles of the left-side head are included.
Second type of raster line (L6 and L8 in FIG. 2) in which only dots formed by the nozzles of either of the right-side head and the left-side head are included.
As illustrated in FIG. 1, the recording unit U may be inclined from the sub-scanning direction Y with a rotation axis as the center by various causes such as a manufacturing error or a use status, for example (that is, the recording unit U may be in a state where a nozzle line of the recording head Hd is not parallel to the sub-scanning direction Y). The rotation axis is parallel to the depth direction Z. In this manner, in a case where the recording unit U is inclined from the sub-scanning direction Y, a position of the right-side head in the recording unit U is uniformly shifted from a position of the left-side head to an upper side or a lower side of the sub-scanning direction Y, in comparison to a position of the right-side head in a case of being parallel.
In a case where printing by the above-described full-overlap method is performed by using the recording unit U which is in a state where the positions of the right and left heads are shifted from each other, a space between the first type of raster line and the second type of raster line becomes ununiform. For example, in the example of FIG. 2, a space IN4 between the first type of raster line L5 and the second type of raster line L6 is smaller than a space IN1 between first type of raster lines L1 and L2 or a space IN2 between first type of raster lines L2 and L3. Similarly, a space IN5 between the second type of raster line L6 and the first type of raster line L7 is larger than the space IN1 or IN2. As described above, Area 2 in which the spaces between the raster lines are not uniform is shown on the print medium, as a banding unevenness (band-like density unevenness). Thus, Area 2 is not preferable.
Such a problem commonly occurs in a case where two or more (for example, three) recording heads are disposed parallel to each other in the main scanning direction of the recording unit.
Thus, in a recording apparatus which performed printing with a recording unit in which a plurality of recording heads is disposed in zigzag, by using the full-overlap method, it is desirable that occurrence of the banding unevenness is suppressed.